Japanese Unexamined Patent Application Publication 2005-258344 describes an image-forming apparatus in which a process cartridge is configured in a freely attachable/removable manner with respect to the unit casing (body frame) of the image-forming apparatus. A drum frame including the casing of the process cartridge is configured in a manner allowing the developing cartridge to be installed in a freely attachable/removable manner. Within the drum frame there are contained a photosensitive drum and a scorotron-type charger.
The photosensitive drum includes a grounded drum unit and a photo-conducting layer formed on the surface of the drum unit. The scorotron-type charger is disposed upward from the photosensitive drum and separated by a predetermined gap. The scorotron-type charger is configured so as to charge uniformly the surface of the photosensitive layer of the photosensitive drum (“surface of the photosensitive drum” hereinafter). After the surface of the photosensitive drum is charged uniformly by the scorotron-type charger, an electrostatic latent image is formed on by exposing the surface based on the image information.
The developing cartridge is equipped with a toner housing which houses a toner serving as a developing agent. In the developing cartridge there are also housed a developing roller, a supply roller, and a toner layer thickness-regulating blade.
The developing roller is configured so as to be able to carry the charged toner at its periphery. The developing roller is configured so as to allow the toner in a pattern corresponding to the electrostatic latent image to be adhered to the surface of the photosensitive drum by being brought into contact with the surface of the photosensitive drum whereon the electrostatic latent image is formed. In other words, the developing roller is configured so as to allow the electrostatic latent image to be developed by the toner carried at the periphery of the developing roller.
The supply roller is configured so as to be able to supply the toner to the developing roller. The toner layer thickness-regulating blade is configured so as to be able to regulate the amount of the toner carried on the periphery of the developing roller to which the toner is supplied by a developing agent supply unit.
The image-forming apparatus is also configured so as to allow a predetermined developing bias voltage to be applied between the developing roller and the grounded, photosensitive drum. Specifically, an electrode electrically connected to the output terminal of a high-voltage circuit is provided in the unit casing. The electrode is configured so as to be able to supply electric potential to the developing roller via a bearing member at the rotation drive central axis of the developing roller by pressing on the bearing when the process cartridge in which the developing cartridge is attached is itself attached to the unit casing.
Image-forming by a conventional image-forming device provided with such a structure is carried out as follows.
First, the surface of the photosensitive drum is charged uniformly by the scorotron-type charger. Next, the electrostatic latent image is formed by exposing the surface of the uniformly charged, photosensitive drum based on the image information.
Then, the surface of the photosensitive drum whereon the electrostatic latent image is formed confronts the periphery of the developing roller whereon the charged toner is carried. The toner in a pattern corresponding to the electrostatic latent image is thereby adhered to the surface of the photosensitive drum. In other words, an image produced by the toner (developing agent image) is formed on the surface of the photosensitive drum. An image is formed on the surface of a recording medium by transferring the developing agent image to the recording medium.